1. Field of the Invention
The invention relates generally to static gaskets for use in sealing a clamped joint such as that of an intake manifold for an internal combustion V engine.
2. Related Art
So-called Liquid Elastomer Molding (LEM) gaskets are generally known, and usually consist of a metallic core, coated over selected areas on both sides with a thin layer of silicone with molded-in sealing beads. These beads have a thread-like quality and are usually formed with differing heights and widths depending on the clamping load distribution and application requirements. An example of a typical prior art LEM gasket is illustrated in FIG. 3. The base elastomer coating provides a good overall micro-seal, and the silicone beads ensure optimum sealing in critical areas. LEM gaskets can be designed with molding along an edge either for sealing of high pressure fluids or for T joints between mating flanges.
The joint between an intake manifold and the cylinder heads of an internal combustion V engine can be difficult to seal. Specialty gaskets of complex design and expensive construction are usually specified for this particular application. LEM gaskets have not heretofore been adaptable to this particular application. In particular, the intake manifold in a V engine is positioned between and bolted to upwardly facing ceiling surfaces of the cylinder head, which portions of the cylinder head comprise intake ports for air fuel mixtures received through the intake manifold. Intake manifold gaskets are installed between the sealing surfaces of the cylinder heads and the manifold and, when clamped, serve to perfect a fluid-tight seal at the joint. The general construction is illustrated in FIG. 1.
Difficulties can arise in this region when the surfaces of the cylinder heads are misaligned. Misalignment can occur as a result of stack-up tolerances from the various parts being bolted together that results in the sealing surface of one or both of the heads being out of the predetermined, ideal position. For example, an ideal position may call for the sealing surfaces of the heads to lie in a common plane, as illustrated in FIG. 1. Alternatively, in different engine designs, an ideal position may call for the sealing surfaces of the head to lie in v-shaped intersecting planes, where the intersection of the two planes falls precisely along the center-line of the engine. The intake manifold, in turn, will have sealing surfaces that rely on the cylinder heads to be properly oriented in order to provide full surface-to-surface support for the gaskets and thus achieve a fluid-tight seal. However, when the sealing surfaces are misaligned, such as indicated schematically in FIG. 6, a step is created in the otherwise aligned support surfaces for the intake manifold gasket, which misalignment leads to irregular loading of the gasket and potential difficulties in achieving an adequate seal.
The problem is made worse by the unpredictable variation in the sealing conditions that can occur in the manufacture of engines. Internal combustion engines are, of course, made by assembling hundreds of components in an assembly operation. Often, the assembly operation is performed in high-production, high through-put factories, where one engine after another is assembled along a working conveyor line. The stack-up tolerances may result in the sealing surfaces of one engine being in proper alignment, whereas the next engine on the assembly line may have one of the sealing surfaces stepped upwardly from an ideal arrangement, while the next engine after that on the assembly line may have one of the sealing surfaces stepped down from the ideal plane, and so forth. This ever-changing, unpredictable environment presents a real challenge to gaskets that rely on parallel meeting surfaces to achieve a fluid-tight seal.
U.S. Pat. No. 5,530,575 discloses a gasket having a thin metal core and elastomer sealing beads applied to each side of the core. This is an example of an LEM gasket, which is well suited to many applications and is relatively inexpensive to manufacture. Unfortunately, this type of gasket construction has difficulty sealing in applications where the two mating surfaces do not have a predictable orientation relative to one another. In other words, if the two mating surfaces can be predicted to always have a parallel planar, or consistently skewed, orientation relative to one another, the height of the sealing beads can be designed to accommodate the anticipated conditions. However, as described above, in the situation of assembling an intake manifold onto a V engine, the orientation between the mating surfaces cannot be predicted with any degree of confidence. As a result, V engine applications have not been able to take advantage of the efficient, low cost and highly desirable LEM gasket construction.
Accordingly, there is a need to adapt LEM gasket construction and methodology to applications in which the orientation of the mating sealing surfaces is not consistent or predictable.